Funding Sources:

Pioneer Hi-Bred International, Inc.

Purdue University Crop Diagnostic Training & Research Center.

Project Description:

Previous reports from the seed industry and some grain farmers suggested
that grain yield of mature corn can mysteriously 'disappear' when the grain is
allowed to dry normally in the field prior to harvest. During the course of a
four-year study (1991-94) designed to investigate the effects of delayed
planting on corn hybrids' seasonal GDD requirements, we measured kernel dry
weight of grain samples harvested twice weekly beginning at near 40 % grain
moisture content and ending at grain moisture contents below 20 %. On each
sampling date, five ears were randomly harvested from three replications each of
three corn hybrids (Pioneer brands 3527, 3394, and 3245).

The approximate developmental stage of the kernels was determined by
visually scoring the development of kernel black layer of 20 kernels removed
from the center of each ear. Once physiological maturity occurred for any given
plot, black layer scoring ceased. The remainder of the shelled grain from the
five ears was thoroughly mixed, grain moisture content was estimated with a
Dickey-john GAC 2000 electronic moisture meter, and the number of kernels in a
200 gram subsample was counted. Thousand kernel dry weight was calculated from
the grain moisture content and the number of kernels in the 200 gram subsample.
Grain sampling in the field ceased when grain moisture content decreased to less
than 20 %. The field study was conducted at the Purdue University Agronomy
Research Center, near West Lafayette in westcentral Indiana.

Results:

Physiological maturity of the corn kernels, defined as the point of maximum
kernel dry weight, occurred at an average grain moisture content of 28.4
percent, and ranged from 25 to 35 percent during the course of the study.
Maximum kernel dry weight averaged 317 grams per thousand kernels. Maximum
kernel dry weight usually preceded the occurrence of a distinct kernel black
layer, more often coinciding with a distinct kernel brown layer.

During three of the four years of the study, kernel dry weight of mature
corn grain of all three hybrids decreased during drydown periods in the field.
The rate of dry weight loss among years and hybrids ranged from 0.6 to 1.6
percent per point decrease in grain moisture content.
Figure 1 illustrates the changes in kernel
dry weight for Pioneer brand 3527 as grain moisture content decreased from about
37 % to about 16 % in 1994 at the Purdue Agronomy Research Center in westcentral
Indiana. Kernel dry weight increased until physiological maturity occurred at
about 25 % grain moisture content. During the post-maturity drydown interval,
kernel dry weight decreased at a rate equivalent to 1.1 % per point decrease in
grain moisture content.

During the three years where kernel dry weight losses were observed, the
average rate of kernel dry weight loss, per thousand kernels, was about 3.4
grams (or about one percent) per point decrease in grain moisture content
(Table 1). The average percent loss in kernel dry weight for the three hybrids
ranged from 0.9 to 1.3 % per point of grain moisture decrease. Kernel dry
weight losses each year, averaged across hybrids, ranged from zero
(nonsignificant) in 1993 to 1.2 % loss per point drydown in 1992 (Table 1). No
significant changes in kernel dry weight were observed in 1993 for any of the
three hybrids.

Bottom Line:

The results of this study support earlier claims made by the seed industry
and farmers that grain yield can 'disappear' when corn is allowed to remain in
the field to dry after physiological maturity has occurred. Our data suggest
that the potential rate of yield loss averages nearly one percent per point
decrease in grain moisture content. Thus, if mature grain were allowed to dry
down ten percentage points in the field (say, from 28 % to 18 % grain moisture
content), the potential yield loss would be ten percent.

The data reinforce the long-held notion that optimum grain moisture content
for harvest is near 25 %. Harvesting grain at moistures much greater than this
often results in damaged kernels, while harvesting at moistures less than this
often results in increased mechanical harvest losses (ear droppage, kernel
shattering). Our data suggest that additional yield loss, beyond that due to
mechanical harvesting, can occur if grain is allowed to dry in the field once
physiological maturity has occurred.